A medical device is disclosed and more specifically a drug delivery pump either attached to or implanted into a patient that infuses a therapeutic substance.
The medical device industry produces a wide variety of electronic and mechanical devices for treating patient medical conditions. Depending upon the medical condition, medical devices can be surgically implanted, connected externally to the patient receiving treatment, or used during surgery. Clinicians use medical devices alone or in combination with drug therapies and surgery to treat patient medical conditions. For some medical conditions, medical devices provide the best, and sometimes the only, therapy to restore an individual to a more healthful condition and a fuller life. One type of medical device is a drug delivery pump.
A drug delivery pump can be attached to or implanted into a patient, and it infuses a therapeutic agent such as a drug or infusate at a predetermined infusion rate and location to treat a condition such as pain, spasticity, or other medical conditions. Drug delivery pumps use a metering device to measure the amount of drug being infused. Some metering devices directly meter the drug being infused by passing the drug through a flow restriction. Since drugs typically have a viscosity about that of water, the flow restriction is often very small to achieve an appropriate infusion rate. Small flow restrictions are difficult to manufacture, prone to clogging, and can apply shear forces to the drug being metered. In addition to flow restriction, there are also other complex direct or indirect metering devices. These complex devices can require significant residential space, battery power, and moving parts such as pumps, gears and other actuators that can be found in peristaltic pumps, electrically operated valves and pumps, and microelectromechanical machined (MEMs) components. Complex metering devices are more expensive to manufacture than simpler devices and can be less reliable and less safe due to their complexity, susceptibility to clogging, alteration of the drug being infused, and creation of significant drug dead space. A less complex, safer, reliable, and low cost metering system is desirable.
A drug delivery pump has an hydraulic metering system that is isolated from the drug. The drug delivery pump has an hydraulic reservoir that is disposed in a housing for containing an hydraulic fluid. A metering device without moving parts is in fluid contact with the hydraulic reservoir and controls the rate that the hydraulic fluid flows from the hydraulic reservoir into a displacement reservoir. The displacement reservoir receives the hydraulic fluid flowing through the metering device, and the displacement reservoir applies pressure to compress a drug reservoir. The drug reservoir is compressible and designed to contain a therapeutic substance such as a drug. A drug infusion port is coupled to the drug reservoir and when the drug reservoir is compressed the therapeutic substance is infused through the drug infusion port.
In another aspect of the invention, the drug delivery pump with hydraulic metering is filled by inserting a filling device containing drug into a drug fill port. Drug fills the drug reservoir and compresses hydraulic fluid in a displacement reservoir. The compressed hydraulic fluid raises pressure in the displacement reservoir which opens a relief valve between the displacement reservoir and the hydraulic reservoir. Hydraulic fluid flows from the displacement reservoir into the hydraulic reservoir. Once the displacement reservoir pressure is below the relief valve relief pressure, the relief valve closes. In still another aspect of the invention, the drug pump begins operation by compressing the hydraulic reservoir causing hydraulic fluid to flow into a metering device. Hydraulic fluid flow is metered to control its flow rate as the hydraulic fluid flows through the metering device and fills the displacement reservoir. The displacement reservoir then applies pressure to the drug reservoir compressing the drug reservoir. Drug is infused as the drug reservoir is compressed.